The need for additional bandwidth has prompted the replacement of traditional electronic links with optical links for applications as diverse as data centers, supercomputers, embedded computing processor-memory interconnects, and fiber-optic access networks. For applications such as these, the silicon photonics platform can deliver necessary bandwidth and, by leveraging its compatibility with complementary metal-oxide-semiconductor (CMOS) fabrication, an economy of scale. In particular, silicon microring resonator based devices exhibit high metrics on size density, energy-efficiency, and ease of wavelength-division-multiplexed (WDM) operation.
Microring sensors are optical resonators that utilize certain properties of light to provide a better, more effective sensor. With their small footprint, CMOS-compatible fabrication, and multiplexed operation, silicon microring resonators are ideal for use as measurement devices. Microring sensors' high-refractive index provides them with a high sensitivity to such environmental factors such as temperature, and they can be treated to be reactive to biological and chemical components, making them useful as small label-free biological/chemical sensors.
FIG. 1 illustrates a microring-based photonic network known in the art for transcribing electrical data signals into the optical domain, transmitting and routing them as necessary, and converting the optical signals back to the electrical domain at the termination of the link. The link includes a multi-wavelength laser source. These laser wavelengths are individually modulated by cascaded microring modulators in a multiplexed configuration. The entire set of signals can then be routed as necessary by microring-based switches. Finally, they can be received by a microring array that de-multiplexes the individual signals before receiving them on independent photodetectors.
The relatively high thermo-optic coefficient of silicon combined with the wavelength selectivity of microring resonators lends them susceptible to changes in temperature and laser wavelength. Additionally, fabrication tolerances can result in microring resonators that are initially offset from their designed operating wavelength. Integrated heaters can be used to tune and stabilize the microring resonance to the laser wavelength. However, for commercial implementations, an energy-efficient and scalable solution to lock and stabilize microring resonators is required.
The use of microrings in interconnects can present challenges due to the difficulty in wavelength-locking them to lasers. A routine procedure for using the microring resonator as a sensor is to probe the resonance shift of the resonator as it is exposed to the environment or sample, and measuring this resonance shift by conducting fast spectral scans with a tunable laser and photodiode, or a broadband source, monochromator, and photodiode. However, the use of costly, bulky, and sensitive equipment such as tunable lasers and monochromators can lead to reduced deployment of microring resonators.
Further, in order to probe the microring sensor, complex and costly spectral scanning equipment can be required. In addition, the spectral scanning equipment can be large and contain sensitive grating components that yield less than robust sensing. Information gathered from spectral scanning equipment can require post-processing, which in turn relies on an added layer of software.
Accordingly, a technique using simple electronics is needed to provide a low-cost and energy-efficient solution that can be scaled to the hundreds to thousands of microrings that would comprise either a future optical interconnect or a large-scale microring sensor array.